1. Field of the Invention
The present invention relates to a method of manufacturing a lithographic mask such as a photomask to be used for manufacturing a semiconductor device and the lithographic mask, and to a method of manufacturing a lithographic mask to be used in an exposing device utilizing such high power exposing means as to promote the forming reaction of an ammonium sulfate type foreign matter, for example, an exposed light constituted by a laser beam having a wavelength of 200 nm or less such as an ArF excimer laser beam, and the lithographic mask.
2. Description of the Related Art
In the formation of a transfer pattern in the manufacture of a semiconductor device, for example, an exposed light is irradiated on a resist through a photomask (reticle), for example. In such a case, there has conventionally been used a photomask in which a shielding film pattern is formed on a transparent substrate. For the material of a shielding film, generally, a chromium type material (a chromium simple substance, chromium containing nitrogen, oxygen and carbon, or a laminated film formed by these material films) is used. In recent years, furthermore, a phase shift mask has been used practically in order to enhance the resolution of the transfer pattern.
Phase shift masks of various types have been known (an alternative type, an auxiliary pattern type and a self-alignment type). For one of them, there has been known a halftone type phase shift mask which is suitable for the high resolution pattern transfer of a hole and a dot. In the halftone type phase shift mask, a semitranslucent film pattern having a phase shift amount of approximately 180 degrees is formed on a transparent substrate, and the semitranslucent film is formed as a single layer or a multilayer.
For example, JP No. 2966369 disclosed a semitranslucent film pattern which is constituted by a thin film formed by a substance containing, as a main component, a metal such as molybdenum, silicon and nitrogen. The semitranslucent film constituted by the materials is formed by a single layer and can control a predetermined phase shift amount and transmittance, and furthermore, is excellent in an acid resistance and a light resistance.
As described above, there has been considerably developed the film material to be used in the photomask which contains nitrogen in the film for various reasons.
When a pattern transfer is to be carried out by using the photomask (reticle), a laser beam is irradiated on the photomask. For this reason, there is a problem in that the formation of some deposit is promoted by a laser irradiation and the deposit becomes a foreign matter to stick onto the photomask. It has been confirmed that one of the deposits is ammonium sulfate.
For the photomask, generally, cleaning (including a resist stripping treatment and a treatment for removing a pellicle adhesive) using a liquid detergent containing S (sulfur) such as sulfuric acid (which will be hereinafter referred to as a sulfuric acid type detergent) is carried out for the resist stripping, the cleaning and the removal of the pellicle adhesive. However, it has been found that a sulfuric acid component derived from the sulfuric acid type detergent used at the cleaning step described above is adsorbed into a photomask surface and is removed with difficulty, and therefore, the sulfuric acid component remains in the photomask after the cleaning. It has been confirmed that these residues are different from each other depending on a pellicle or an environment for use and chemically react to an ammonia component in the air to form and deposit ammonium sulfate in the state of a crystal. Moreover, there was inspected a material containing nitrogen which is used for a thin film to be utilized in the photomask. As a result, it has been found that more ammonium ions (NH4+) are present on the surface of a thin film containing nitrogen than a thin film which does not contain the nitrogen. Accordingly, it can also be supposed that the nitrogen component in the thin film to be used in the photomask might contribute to the deposition of the ammonium sulfate which can be a foreign matter defect.
With the microfabriation of an LSI pattern in recent years, particularly, the wavelength of an exposed light source (the wavelength of an exposed light) has increasingly been reduced from an existing KrF excimer laser (248 nm) to an ArF excimer laser (193 nm) and an F2 excimer laser (157 nm). In such a situation, for example, in the case in which an exposed light source having a short wavelength such as the ArF excimer laser is used, a laser output becomes high. Therefore, there is a problem in that the formation of a deposit can be promoted more easily and a foreign matter is generated more remarkably, resulting in a great influence on quality.
In the case in which the deposition of the ammonium sulfate is recognized on the surface of the photomask, a quality abnormality is caused so that it is necessary to carry out cleaning or fabrication again.